1. Field of the Invention
Present invention relates, in general, to vehicle windshield wipers, and, more particularly, to windshield wiper park switches.
2. Description of Related Art
In vehicle windshield wiper drive apparatus, the wipers are provided with an automatic home or park position stop device which enables a wiper blade to return to the home position regardless of when a user turns off a wiper switch during the wiping cycle.
In a typical wiper park switch, an electrically conductive plate is provided with electrically conductive and electrically non-conductive portions or traces. An electrical contact(s) fixed to or otherwise driven by a drive gear coupled to the wiper drive motor cooperates with the electrically conductive plate to form a switch when opens and closes an electric circuit of the wiper drive motor so that even when the user turns off the wiper switch of the vehicle during the wiper cycle, the electrically conductive plate and the contact(s) form an electric circuit which enables the wiper blade to return to the park position. The contacts are typically driven or moved by the gear between two positions, one forming a closed switch with the electrically conductive plate and the other forming an open circuit. When opening the electric circuit to the motor, the contact(s) shorts the circuit to form a dynamic brake which quickly stops the wiper arm at the park position.
However, prior vehicle windshield wiper drive mechanisms of this type experience several problems. First, the single park switch contact is moved into and out of contact with the conductive traces on the conductive plate many times during a wiping operation. This causes wear of the contact and requires a more robust wiper and contact design which adds to the cost of manufacturing the vehicle wiper.
Second, prior wiper driving apparatus with conventional park switches frequently experience chatter when snow or another obstruction is disposed over a lower portion of the vehicle windshield preventing the wiper blade from returning to the park position. In this situation, the drive gear of the wiper motor is subjected to a force which acts in a direction counter to the normal rotation direction of the drive gear. When the wiper arm contacts the snow or obstacles, forces build in the arm which reverse rotates the drive gear. Since the park switch is connected directly to the drive gear rotated by the drive motor, the park switch also reverses direction again completing a circuit to the motor. This results in so-called xe2x80x9cchatterxe2x80x9d wherein the wiper drive motor is sequentially energized and de-energized at a rapid rate leading to a quick rise in the motor operating temperature and/or rapid deterioration of the park switch contact.
Thus, it would be desirable to provide a park switch for a vehicle wiper apparatus which overcomes the above-mentioned problems encountered with previously devised wiper park switches. It would also be desirable to provide a park switch for a vehicle wiper drive apparatus which can be constructed with a minimal number of components. It would also be desirable to provide a park switch for a vehicle wiper drive apparatus which minimizes wear to the movable contacting portions of the park switch. It would also be desirable to provide a park switch for a vehicle wiper drive apparatus which prevents xe2x80x9cchatteringxe2x80x9d even if the wiper arm strikes an accumulation of snow or other obstacles preventing the wiper arm from moving to the park position.
The present invention is a park switch bridge for use in a wiper driving system.
According to one aspect of the present invention, the wiper drive apparatus includes a drive motor and a drive gear disposed in a housing. A lead frame is fixed within the housing and includes a plurality of discrete, electrically conductive tracks. A park switch bridge is rotatably mounted in the housing and engagably coupled to the drive gear for rotation with rotation of the drive gear. The park switch bridge includes a plurality of spaced contacts, each contact slidable over the conductive tracks to open and close a circuit to the drive motor upon rotation of the park switch bridge.
A park switch bridge drive or engagement member is carried on the drive gear and engages the park switch bridge upon rotation of the drive gear. The engagement member and the park switch bridge are arranged in intersecting, rotatable paths of movement such that each revolution of the drive gear causes engagement of the drive member with the park switch bridge to rotate the park switch bridge through a predetermined arc.
In one aspect of the invention, the contacts extend radially from a center portion of the park switch bridge.
Preferably, four contacts are provided on the park switch bridge equidistantally spaced substantially 90xc2x0 apart.
According to another aspect of the invention, each contact is resiliently carried on an arm having one end at the center portion of the park switch bridge and an opposed outer end. According to another aspect of the present invention, a beam is cantilevered from each arm and carries the contact. In one aspect, the contact is unitarily formed as an integral part of the beam from the beam material. In another aspect of the invention, the contact is in the form of a pad fixedly mounted on the beam. Each beam projects from the plane of each arm to resiliently bias the contacts into engagement with the conductive tracks on the lead frame.
Each arm has a planar portion extending from the center portion and a raised sidewall extending along at least a portion of the peripheral edge of the planar portion. The drive or engagement member carried on the drive gear rotatingly engages the raised sidewall on each arm to rotate the park switch bridge upon rotation of the drive gear.
The park switch bridge of the present invention provides several advantages over previously devised park switches used in wiper driving apparatus. The provision of a plurality of contacts, such as four circumferentially spaced contacts on the park switch bridge, reduces contact wear compared to the single contacts used in prior art park switches by distributing contact wear substantially evenly over four contacts.
Also, the park switch bridge of the present invention, is unidirectionally coupled to the drive pin on the drive gear for rotation in only one direction. Thus, back driving or reverse rotation of the drive gear as caused by the wiper arm contacting an accumulation of snow or other obstacles on the lower portion of the vehicle windshield preventing the wiper arm from fully reaching the park position, does not result in reverse rotation of the park switch bridge which has heretofore resulted in xe2x80x9cchatteringxe2x80x9d or a rapid on and off application of electric power of the wiper motor leading to contact deterioration and/or motor overheating. This arrangement also prevents the park switch bridge from being stranded in an operation position due to reverse rotation.
The present park switch bridge, by distributing contact wear over a plurality of contacts, such as four contacts, enables the contacts to be inexpensively formed from the spring beam material itself without exceeding a beam thickness which would adversely affect the spring properties of the bridge, or risking contact wear that is greater than the base material thickness.
Finally, the park switch bridge of the present invention, the lead frame, the drive gear and the drive pin can be readily mirrored for opposite oriented motor designs.